The following disclosure relates generally to brake systems for holding wing flaps and other aircraft control surfaces in position, and to methods for using such brake systems.
All aircraft include movable control surfaces for directional control in flight. Such control surfaces can include ailerons for roll control, elevators for pitch control, and rudders for yaw control. In addition, most conventional jet transport aircraft typically include leading edge slats and trailing edge flaps on the wings.
These devices can be used to generate high lift during takeoff and landing when the aircraft is traveling at relatively low air speeds.
Federal aviation regulations (FARs) impose airworthiness standards on lift and drag devices for transport category aircraft. For example, FAR xc2xa725.697 requires that such devices (e.g., trailing edge flaps) must maintain selected positions (e.g., extended positions) without further attention by the pilot. This requirement applies at all times during flight. Thus, lift and drag devices must be able to maintain extended positions even during a general failure of the aircraft""s power system. Applicant further understands that future FARs will require periodic testing of lift and drag devices to demonstrate their ability to maintain selected positions under flight loads without power and without pilot input.
Trailing edge flaps (xe2x80x9cflapsxe2x80x9d) on jet transport aircraft typically deploy aft of the wing and downward to increase wing area and camber. The flaps are typically powered by a drive shaft that extends longitudinally inside the wing and is coupled to a central power drive unit. The drive shaft is connected by a system of gears to a series of ball screws distributed along the length of the wing adjacent to the flaps. Rotation of the drive shaft in a first direction causes the ball screws to rotate in a corresponding direction, thereby extending the flaps. Similarly, counter rotation of the drive shaft causes the ball screws to counter-rotate, thereby retracting the flaps.
Conventional brake systems for holding flaps in position include xe2x80x9cno-backxe2x80x9d brake systems and xe2x80x9cwing-tipxe2x80x9d brake systems. Both of these systems are xe2x80x9cactivexe2x80x9d brake systems that actively engage the flap deployment system to hold the flaps in a selected position and actively release the flap deployment system for flap repositioning. A typical wingtip brake system, for example, includes a friction brake that engages the drive shaft when the flaps are fully extended to hold the flaps in the extended position. For flap retraction, the wing-tip brake releases the drive shaft so the power unit can rotate the drive shaft in the counter direction and retract the flaps.
One shortcoming of conventional flap brake systems is the difficulty in testing the ability of the brake to hold the flaps in a selected position. Another shortcoming of such systems is that they typically do not include means for determining the health of the system. That is, such systems typically do not include means for determining the amount of useful life remaining on the system components before one or more of the components should be replaced or refurbished. As a result, these components are typically replaced as a matter of course well before the end of their useful life.
Aspects of embodiments of the invention are directed to brake systems for aircraft control surfaces such as leading edge slats and trailing edge flaps. In one embodiment, an aircraft system for moving a control surface between an extended position and a retracted position includes a movable member and a brake. The movable member can be operably coupled to the control surface such that the control surface moves from the extended position toward the retracted position in response to movement of the movable member in a first direction. The brake can be configured to resist movement of the movable member in the first direction when the control surface is in the extended position. The brake can be further configured to resist movement of the movable member in the first direction when the control surface moves from the extended position toward the retracted position. In one aspect of this embodiment, the aircraft system can further include a force sensor operably coupled to the brake that is configured to measure a force applied to the brake as the control surface moves from the extended position toward the retracted position. A memory device can be operatively coupled to the force sensor that is configured to record the force applied to the brake as the control surface moves from the extended position toward the retracted position.
In another embodiment, a method for operating an aircraft control surface can include activating a control system to move the control surface from a retracted position to an extended position. Once in the extended position, a brake can be applied to the control system to at least restrict motion of the control surface from the extended position. The method can further include activating the control system to move the control surface from the extended position to the retracted position. While the control surface is moving from the extended position to the retracted position, the brake can continue to be applied to the control system to resist the movement of the control surface from the extended position to the retracted position.